1. Field of the Invention
The present invention relates to an ink jet recording head adapted for use in an ink jet recording apparatus for executing recording operation by discharging liquid such as ink, and a producing method therefor. The present invention is applicable not only to an ordinary printing apparatus but also to an apparatus such as a copying apparatus, a facsimile apparatus provided with a communication system or a work processor provided with a printing unit, or to a multi-function recording apparatus formed by complexing these apparatuses.
2. Related Background Art
The ink jet recording apparatus is a recording apparatus of so-called non-impact recording method, and has various features such as high speed recording, ability of recording on various recording media and scarce noise generation at the recording. For these reasons, the ink jet recording apparatus is widely employed in the recording mechanism of the printer, copying apparatus, facsimile, word processor etc.
As the representative ink discharging method in a recording head mounted on such ink jet recording apparatus, there is known a method of employing an electromechanical converting member such as a piezo element, a method of generating heat by irradiation of an electromagnetic wave for example with a laser and discharging an ink droplet by the action of such heat generation, and a method of heating ink by an electrothermal converting element having a heat generating resistance member and discharging an ink droplet by the action of film boiling. In an ink jet recording head employing the electrothermal converting element, such element is provided in a recording liquid chamber and is given an electric pulse constituting a recording signal to provide the ink with thermal energy, and the pressure of a bubble generated in the recording liquid (at the boiling thereof) resulting from a phase change therein to discharge a small ink droplet from a small discharge opening, thereby executing recording on a recording medium. In general, such ink jet recording head is provided with an ink jet recording nozzle and a supply system for supplying the nozzle with the ink.
For forming such recording head, there is already known, as disclosed in the Japanese Patent Application Laid-open No. 10-776, there is known a method of adhering and patterning a copper foil of a thickness of 50 microns on a polyimide film, electrically jointing, by thermal ultrasonic pressing, bumps on electrode pads on a recording element to the gold-plated electrode leads (inner leads) of thus formed TAB (tape automated bonding) tape, then sealing the jointed portion and adhering the assembly to a substrate. Also the Japanese Patent Application Laid-open No. 9-300624 proposes a method of processing the electrode after bump formation. Also the Japanese Patent Application Laid-open No. 11-138814 discloses a method of connecting plural recording elements to respectively independent TAB tapes and then adhering them to a substrate. In the configuration shown in the aforementioned Japanese Patent Application Laid-open No. 11-138814, there are provided plural recording elements for color printing, but there is also known a recording head which is internally divided so as to enable color printing by a single substrate.
The price of the ink jet recording apparatus is recently showing a remarkable reduction, so that the major issue is how to produce the ink jet recording head inexpensively. For this purpose, most effective is the reduction of the material cost of the component parts, particularly the integration of the substrate for the recording element, and there is widely employed a method of integrating the substrates of the recording elements for the inks of yellow, megenta and cyan colors. There are also employed a method of integrating the substrate of the recording element for the black ink frequently used for character printing with the aforementioned substrate of the color recording elements and a method of incorporating the substrate of the color recording elements and the substrate of the black recording element into a same recording head. For example the Japanese Patent No. 2839686 discloses a method of mounting plural different recording element substrates on a single TAB tape as an example of the driving semiconductor device. Such mounting method is to constitute a circuit by mutually connecting plural recording element substrates. However, in the configuration of connecting the plural recording elements respectively to the independent TAB tapes and then adhering to the support member as disclosed in the Japanese Patent Application Laid-open No. 11-138814, it is necessary to align each TAB tape with the support member at the adhering operation, while the recording apparatus inevitably becomes bulky since the recording elements cannot be positioned mutually very close, and the capping mechanism, for preventing liquid evaporation in the non-recording state, has to be made independent for each recording element. Furthermore, since a component, in which the TAB tape and the recording element are combined, has to be adhered to the support member, it is difficult to fix the recording element to the support member with sufficient precision. In case plural recording elements are present, it is even more difficult to adhere such recording elements with sufficient relative precision. Also since an operation of sealing the electrode leads (inner leads) with resin has to be executed in the air, the sealing agent ordinarily employed in the TAB technology may flow to and clog the discharge opening for discharging the recording liquid, or the inner leads may be exposed if the amount of the sealing agent is reduced in order to prevent such clogging phenomenon. Furthermore, the resin for sealing the inner leads may flow to the back side of the recording element so that some of the recording elements may become unable to be fixed.
Also in case of assembling the black ink recording element substrate and the color ink recording element substrate within a same head, it is necessary to mutually align the relative position of the respective liquid discharge openings. However, if an inner lead bonding step, for jointing the electrodes of a semiconductor chip with the inner leads (electrode leads) protruding in a device hole (aperture) provided in the film carrier tape, and a step of sealing the inner leads with resin, both steps being common in the TAB technology, are executed prior to the assembly of each recording element substrate into the head, the precision of the relative positional relationship of the discharge openings may be deteriorated to result in significant mutual blotting of the black ink and the color inks or in mutual positional displacement thereof at the ink jet recording operation.
Now there will be given an explanation on the conventional recording element unit with reference to FIGS. 24 and 25, which show, in the conventional TAB mounting process, a method of electrically jointing bumps on the electrodes of the recording element to the electrode leads of an electric wiring tape by thermal ultrasonic pressing, then sealing the jointed portion and adhering it to a support member.
In the conventional configuration shown in FIGS. 24 and 25, an electrical wiring tape H300 has a three-layered structure in the vicinity of the bonding portion, consisting of a polyimide base film H300a at the top side, a copper foil H300b in the middle and a solder resist H300c at the rear side. The electrical wiring tape H300 is provided with a device hole (aperture) H11 in which a recording element substrate H100 is inserted and a device hole H12 in which a recording element substrate H101 is inserted, and, in such holes, there are exposed gold-plated electrode leads (inner leads) H302 to be connected to bumps H5 of the recording element substrate H100 or H101.
In the first recording element substrate H100 and the device hole H11 of the electrical wiring tape H300, the conventional TAB mounting method is used to align the electrode leads H302 of the electrical wiring tape (TAB tape) H300 with the bumps H5 on the electrodes of the recording element H100, then to execute electrical jointing by thermal ultrasonic pressing method and to seal the jointed portion with a sealing agent H308 thereby obtaining a TAB unit H300U1. Also, in the second recording element substrate H101 and the device hole H12 of the electrical wiring tape H300, the electrode leads H302 of the electrical wiring tape (TAB tape) H300 are electrically jointed with the bumps H5 on the electrodes of the recording element H100 by thermal ultrasonic pressing method and the jointed portion is sealed with the sealing agent H308 to obtain a TAB unit H300U2. The TAB units are separated because, in the conventional TAB mounting method, it is difficult to obtain the positional precision of the chip (recording element substrate) with respect to the TAB tape after sealing, sufficient for use in the ink jet recording apparatus (particularly color recording apparatus).
Then a second plate H400 is adhered to the first plate H200 by a second adhesion layer H203, of which thickness is limited to 0.06 mm or less in order that the first recording element substrate H100, the second recording element substrate H101 and the electrical wiring tape H300 can be electrically connected in planar manner.
Then a first adhesion layer H202 for adhering the first recording element substrate H100 and the second recording element substrate H101 and a third adhesion layer H306 for adhering the electrical wiring tape H300 are formed by coating respectively on the first plate H200 and on the second plate H400, and the TAB units H300U1 and H300U2 are fixed by pressing with relative positional alignment of the plural recording elements H103 for discharging recording liquids or respective discharge openings H107 along the plane of wiring. In this operation, since the sealing agent H308 is deposited on the upper face (ink discharging surface) of the first and second recording element substrates H100, H101, pressing heads H100H, H101H having suction pipes V110 are limited in the contact areas with the recording element substrates H100, H101 in order to avoid such deposited areas. Also the sealing agent H308 usually stops at the ridge of the recording element substrate and seldom flows to the adhesion surface, but it may occasionally flow to such adhesion surface because of a fluctuation in the viscosity of the sealing agent, and, in such case, the first or second recording element substrate H1100, H101 may become inclined by the thickness of thus deposited sealing agent, thus resulting in an inclined liquid discharge direction or ink leakage.
Subsequently, in order to securely adhere the electrical wiring tape H300 to the second plate H400, the electrical wiring tape H300 is pressed and fixed to the second plate H101 by a tape pressing head T300. In the operation of pressing the first and second recording element substrates H100, H101 for adhesion fixing, the electrical wiring tape H300 and the third adhesion layer H306 are preferably not in mutual contact, because, if the pressing is insufficient, the first and second recording element substrates H100, H101 remain in a floating state to result in an inclined liquid discharge direction or ink leakage.
Furthermore, the ink jet recording head of the above-described configuration including plural recording element substrates which are electrically connected with the electrical wiring tape is associated with the following drawbacks:
(1) When the arrangement pitch of the electrodes becomes smaller for example by a higher density or a higher level of integration of the recording element substrate, there tends to be generated an electrical shortcircuiting in thermal ultrasonic jointing of the electrode terminals of the electrical wiring tape to the bumps on the electrodes of the recording element substrate;
(2) When the number of the recording elements per recording element substrate increases, there increases the number of necessary electrodes, resulting in an increase in the probability of the electrical shortcircuiting mentioned in (1) per recording element substrate;
(3) If the arrangement pitch of the electrodes of the recording element substrate is increased in order to avoid the drawbacks (1) and (2), the size of the recording element substrate itself may be increased to elevate the cost thereof. Also the recording head may become larger to increase the dimension of the recording apparatus, thus eventually increasing the cost thereof; and
(4) In case of aligning the recording element substrate with the support member or aligning the electrode terminals of the electrical wiring tape with the bumps on the electrodes of the recording element substrate, there inevitably result a positional aberration resulting from the fluctuation in the assembling in the aligning operation, and such aberration, if becoming large, may result in electrical shortcircuiting at the thermal ultrasonic pressing of the electrodes and the electrode terminals. The probability of such electrical shortcircuiting varies depending on the aligning position between the electrode terminals of the electrical wiring tape and the electrodes of the recording element substrate.
In consideration of the foregoing, an object of the present invention is, in an ink jet recording head in which plural recording element substrates are adhered to a same support member, to improve the reliability of inner lead bonding and to realize secure electrical connection, by at first adhering semiconductor chips (recording element substrates) to the support member, and then executing an inner lead bonding step (step for jointing the inner leads (electrode leads) protruding in the device hole provided in the film carrier tape and the electrodes of the semiconductor chip) and a step of sealing the inner leads with resin, as already known in the conventional TAB technology.
Another object of the present invention is to provide an inexpensive ink jet recording head capable of high-quality ink jet recording.
By employing metalxe2x80x94metal bonding such as thermal ultrasonic pressing on the bump and the electrode lead, the reliability of connection can be secured even when the bump and the electrode lead are jointed after the recording element substrate and the flexible wiring substrate are fixed to a first support member. Also there can be provided an inexpensive ink jet recording head, since standardized apparatus and technology can be used.
Also by adhering a second support member to the first support member in such a manner that the distance between the upper surface of the second support member and the upper surface of the bumps on the plural recording element substrates becomes constant, there can be provided an inexpensive ink jet recording head of satisfactory reliability. In such operation, by correcting and smoothing the fluctuation in the height of the upper surfaces of the bumps on the plural recording element substrates, there can be provided an ink jet recording head of even higher reliability.
Also by executing the resin sealing of the pointed portions of the bumps on the recording element substrate and the electrode leads of a single flexible wiring substrate after such single flexible wiring substrate is fixed to the second support member, there can be achieved stable resin sealing, thereby providing a more inexpensive ink jet recording head.
Also there can be provided an inexpensive ink jet recording head of high print quality and high realiability, by fixing, with an adhesive material, the plural recording element substrates to the first support member to which the second support member is adhered with an adhesive material, then aligning the electrodes of the recording element substrates with the electrode leads of the wiring substrate, then fixing the wiring substrate to the second support member with an adhesive material, jointing the electrodes of the recording element substrate with the electrode leads of the single flexible wiring substrate and sealing, with resin, the jointed portions of the electrodes of the recording element substrates and the electrode leads of the single flexible wiring substrate.
By executing metalxe2x80x94metal bonding between the bump and the electrode lead, there can be provided an ink cartridge of higher productivity.
Also there can be provided an inexpensive ink jet recording head of high print quality and high reliability, by maintaining a constant distance between the upper surface of the second support member and the upper surface of the bumps and then sealing the metalxe2x80x94metal bonded portions and jointed portions.
Still another object of the present invention is to providing a producing method for an inexpensive ink jet recording head capable of ink jet recording of high quality, in which the defect rate is reduced in the electrical connection between the electrodes of the recording element substrate and the electrode terminals of the electrical wiring tape electrically connected to the recording element substrate, and an ink jet recording head produced by such method.
In connecting the electrode terminals of an external wiring substrate, since the alignment is made between the electrodes of the first recording element substrate, arranged with a smaller first arrangement pitch, and the electrode terminals of the external wiring substrate corresponding to such smaller first arrangement pitch, the electrode terminals of the first recording element substrate with a higher electrical shortcircuiting rate are aligned with better precision and the electrical shortcircuiting rate is reduced in the entire head. Therefore, in electrically connecting the electrodes and the electrode terminals for example by metalxe2x80x94metal bonding, there can be reduced the electrical defects resulting for example from the electrical shortcircuiting, induced for example by the electrode terminal being also connected to an electrode adjacent to the electrode to which the electrode terminal is to be connected.
A reduction in the arrangement pitch of the electrodes of the recording element substrate with a large arrangement pitch of the recording elements allows to compactize the head without influencing for example a functional element for driving the recording element. In such case, the width of the electrode terminals of the external wiring substrate, corresponding to the recording element substrate with a larger arrangement pitch of the electrodes is increased whereby the engagement with the bumps on the electrode terminals can be made larger even if the components are displaced in position by a fluctuation in the assembling, and the rate of electrical defects can be reduced.
Alignment of higher precision can be achieved since the alignment is executed between the electrodes, arranged with a smaller first arrangement pitch, of the first recording element substrate and the electrode terminals of the external wiring substrate corresponding to such smaller first arrangement pitch. It is thus rendered possible to reduce the defects relating to electrical connection, also to improve the production yield thereby achieving reduction in cost.
A reduction in the arrangement pitch of the electrodes of the recording element substrate with a large arrangement pitch of the recording elements allows to compactize the head without influencing for example a functional element for driving the recording element.